The purpose of this proposed study is to determine if present knowledge of spinal cord neurophysiology and of the effects of anesthetics and analgesics upon spinal cord neurons, especially those systems involved in the transmission of noxious information, accurately reflects the systems as they exist in intact animals. With few exceptions, studies dealing with spinal cord physiology and pharmacology have been carried out in either anesthetized or decerebrate animals with or without transected spinal cords. Each of these interventions is used for the specific purpose of altering the normal functioning of the central nervous system. Unfortunately, neither the mechanism of action, nor the total effect any of these techniques is known. It is imperative that we determine whether or not or knowledge of pain pathways within the spinal cord, and our understanding of drug interactions with those pathways represents the situation as it exists in the intact animal or is merely a reflection of artifacts arising from the preparations used in previous studies. This project has two specific goals. The first is to determine, using extracellular single neuron microelectrode recording techniques, the neurophysiological response characteristics of dorsal horn spinal cord neurons in awake, restrained cats following stimulation of peripheral receptive fields with both non-noxious and noxious stimuli. The second goal is to determine dose response effects of selected anesthetics and analgesics upon the neuronal responses of dorsal horn cells in neurophysiologically intact animals. The information obtained from these studies will not only help to clarify the importance of spinal sites in anesthesia and analgesia following systemic drug administration but will also increase our understanding of the neurophysiological response properties of neurons in the dorsal horn of spinal cord.